1. Field of the Invention
The present invention relates to image processing and, more particularly, is directed towards a process which detects the presence of man-made objects in an arbitrary scene using Fourier transform spatial filtering.
2. Description of the Prior Art
The detection of man-made objects in an arbitrary background is of fundamental importance in problems of surveillance, target detection and target tracking. Systems automated to achieve these ends must be able to react in real-time to a changing scene as well as account for aspect and range dependent target profiles. The goals to be achieved can be categorized as object detection, classification, and identification. Detection simply means that an object is observed without any reference to what the object is; classification means that an object has been identified as belonging to a class, such as a tree, a tank, or a man; and identification means distinguishing between objects of the same class, and naming the object such as an oak tree, an M-60 tank, or an American soldier.
Each of these goals require different degrees of shape information. Thus for detection, information on spatial geometry is not necessary but relative size is. For classification, spatial geometry is essential however image resolution requires only silhouette detail. Identification, however, requires resolution sufficient to resolve structural elements internal to the overall silhouette outline.
Real-time optical processors have long been recognized for such potential applications as optical computing, robotic vision, image understanding, and pattern recognition. In particular, optical processors offer a powerful high speed alternative to electronic processors due to their ability to process in parallel a large amount of information. One example is the optical correlator proposed by A. B. Vander Lugt in which prerecorded Fourier filters are used to identify the presence of specific objects. In a modern version of the Vander Lugt processor the photographically stored Fourier filters are replaced by a photorefractive nonlinear optical medium or crystal. The advantage of the crystal approach over traditional wet-chemical processing is that the correlation between different scenes is carried out in near real time and not limited by the time needed for film development or film replacement. Despite the success of modern correlators, however, they are hampered by an old but severe limitation for practical application. Even the modern correlator has not overcome the inability of traditional correlators, using matched filters, to recognize an object independent of its size or the viewed perspective.